Damage to concrete structures such as roads, runways, bridges, and even buildings is a chronic problem around the world. The natural erosion processes in combination with pollution and/or heavy use have a severe impact on the life of these structures.
Surface damage in concrete roads can result from a number of causes—frost damage, late finishing, toweling-on of a “topping” layer after the main slab has been compacted and found to be low, or mechanical damage, caused for example by vehicles. Concrete can have high void content that can allow moisture to enter the surface and when frozen, produce tensile stresses that result in scaling and cracking of the surface. Additionally, concrete surfaces can scale as a result of using de-icing agents for ice and snow removal. The application of a de-icing agent to a pavement that is already covered in snow or ice will cause the surface to lose heat rapidly. This melts the ice on the surface, but can cause freezing of any moisture that has become trapped in the material, potentially damaging it.
The occurrence of potholes on asphalt and cement pavements have been long standing issues for all transportation agencies in this country as well as around the world. Over the years, improvements in materials, repair deployment methods, and supporting deployment systems have greatly helped to make repairs more durable and economic. However, the life of repaired potholes normally still is counted in terms of days or months, rather than years. The cost of pothole repair to the city and state transportation and maintenance departments and federal agencies are in the range of millions dollars per year. In addition, the existence of potholes presents a great safety hazard to vehicles, structures, and pedestrians. A driver's inherent reaction to veer away from a pothole often presents a danger to nearby vehicles and pedestrians and can cause serious traffic disturbances.
It is felt that the dominating mechanisms in forming potholes are different under different weather or environment conditions, although the presence of water in the sub-base serves as a major reason for potholes formation. Potholes are generally caused by moisture and water percolates through fissures in pavement and collects in the sub-base of the pavement. In colder climates, the subsequent freeze-thaw action pushes the pavement upward while traffic stresses the pavement and a breakdown of the road surface causes a material collapse that forms the pothole. Alternatively, in warmer areas, the freeze-thaw cycle plays a less important role. In places such as Florida, temperature and the impact of water on the integrity of the road material and subsurface combine to reduce the integrity of the surface and lead to its compromise. Additionally, traffic, poor construction, aged concrete, or a combination of these factors also play a role in all areas. Therefore, by limiting the amount of water that percolates through fissures in the road or any subsequent repairs, the deleterious effects of moisture on road quality can be mitigated.
It is felt that the failure and short life of the pothole repairs are due to the creation of precursor cracks as the result of low toughness, low rutting resistance and low strength of the repairs materials. The moisture further assisted the debonding of the binders within the aggregates within the repair material, and the repair materials with the base of the pavement. Therefore, by increasing the dynamic toughness and strength, and eliminate the voids that existed in the repair mixtures which provide paths for moisture penetration, the pothole repair life can be improved substantially.
Similarly, buildings, bridges and other concrete structures are continually impacted by weathering processes primarily catalyzed by water. Water can cause spalling and damage to surfaces of bridges and buildings, exposing structural components, such as steel beams and rebar, that may be further damages and cause even more erosion to the concrete. Further, acid rain can not only cause ugly discoloration to building facades, but also cause significant damage and deterioration to concrete buildings, bridges, and other concrete surfaces, as the acidic solution dissolves the calcium hydrates in the cement. As the current highway system in the United States is both vast and aging, there is clearly a need to find a way to cost-effectively protect the roads and bridges that make up our infrastructure.
On method that has been used for asphalt concrete is polymer modified asphalt (“PMA”). PMA has become common in road paving and roofing and may represents much as 20% of all asphalt used today. Improvements in rutting resistance, thermal cracking, fatigue damage, stripping, and temperature susceptibility have led polymer modified binder to be substituted for asphalt in many paving applications, including hot mix, cold mix, chip seals, hot and cold crack filling, patching, and slurry seal. PMAs are used wherever performance and durability are desired. Asphalt specifiers are finding that many of the Superpave binder grades (Superpave, which stands for Superior Performing Asphalt Pavements, represents an improved, standardized system for specifying, testing, and designing asphalt materials) need polymer modification to meet all the requirements for high temperature rutting resistance and thermal cracking resistance at low temperatures.
A typical design of pothole repair is to raise the surface above that of the road surface, and to overlay the material directly over the road surface, around the perimeter of the repair. This is done to prevent the intrusion of water. Further, the overlaid area must be of sufficient thickness so that fractures do not occur, which can break and dislodge pieces of the repair. While it would be safer to make the repair flush with the road surface, absent a firm watertight bond, this is not possible. It would be desirable to produce a repair that does not produce a bump that can adversely affect motorists. It would further be desirable to have a repair material that does not compress with traffic so that it can be set at the desired height without fear of changing over time.
A typical practice with asphalt repair is to wait long enough for the material to cool sufficiently to harden enough to permit traffic. This can result in long down-times that can be disruptive and costly. It would be an advantage to have a quick-curing thermoset that permits road opening without damage in a relatively short time.
A typical design practice is to raise the pothole repair material above the road surface temporarily, and to count on traffic to reduce it to its desired final height. This can be difficult to estimate, as it can be inexact how much the repair will settle, and in how much time. Weather can be an important variable here, as asphalt repairs settle more and more quickly with heat. It can be appreciated that a repair that ends up too high can cause an unsafe bump for motorists, and a repair that ends up too low can cause pooling of water. It would be an advantage to have a repair material that does not appreciably change after its installation, simplifying the design and removing uncertainty.
Traditionally, polymers used for asphalt modification were typically thermoplastic polymers that could be added to the mix as solids. Normally, such polymer addition involved adding the solid polymer, possibly after grinding, to a rear-shear mixing vessel containing asphalt generally heated above 325° F. for a period of time to assure thorough mixing. However, this tended to be a labor and capital intensive process.
Despite the benefits of adding polymers to asphalt to improve physical and mechanical performance, the polymers currently in use may not optimize asphalt performance. Also, the cost of adding polymers to the asphalt at levels sufficiently high to meet desired specifications can be prohibitive. As a result, the industry has looked for ways to enhance the performance of the polymer modifiers, such as the development of additional chemical agents. Many of these agents have been termed crosslinkers and are believed to either crosslink the polymer to the asphaltene component of the asphalt or crosslink the polymer and improve properties. However, the incorporation of polymers and other components into the asphalt can cause numerous problems that compromise the requisite asphalt properties. Further, these methods are incompatible for use with cement concrete. It is therefore desirable to develop technologies and methods for adding polymers to concrete that produce a concrete with improved durability that doesn't compromise the necessary properties of the material.